The present invention relates to coating compositions for coloring transparent objects, particularly glass objects, and more particularly container such as bottles, jars, and the like. Containers such as glass bottles made of glass of one base color, such as clear, or a small number of base colors may be provided with a wide variety of colors by applying a colored coating to the surface of the bottles. To change the color of the glass forming the body of the container can be costly due to lost production time during the color change. Heretofore, producing containers with a wide variety of colors was generally considered economically unfeasible, and production of a unique color could be justified only by a need for a large quantity. Providing color to containers by means of coatings avoids these constraints because the coating color can be changed much more readily than the color of the body of the containers.
The prior art includes many proposals to coat glass containers for the sake of improving strength and impact resistance was well as for coloration. However, the prior art container coatings have been found to have shortcomings in providing a combination of adhesion, clarity, and color fastness sufficient to withstand subsequent processing to which the containers may be subjected, such as washing, sterilizing, and contact with products during filling operations. Therefore, the present invention relates to improved compositions for providing such surface coloration that is resistant to subsequent process conditions.
Another requirement addressed by the present invention is that colorants in container coatings not contain metallic species that would complicate recycling of the containers. Environmental concerns also make it desirable that coating compositions of this type be water based.
The primary objective of the invention is to provide color to transparent containers for the sake of esthetics, and thus relates to alteration of transmittance of light in the visible wavelength range of about 360 to about 760 nanometers. Optionally, the present invention may provide coatings that also alter transmittance in the ultraviolet region of the spectrum (below 360 nanometers). It has been known that beverages such as beer, ale and the like made from or containing fermented extracts of malt are not stable to light. It is believed that harmful light, particularly in the ultraviolet region, adversely affects the flavor of these beverages in transparent light-transmitting containers and thereby causes a defect known as "lightstruck" flavor. The common art-known method of preventing lightstruck flavor of these beverages entails making the containers brown or dark amber in color. These colored containers are believed to cut out most of the harmful light. Alternatively, the containers can be treated with a delustering agent in order to reflect and diffuse the harmful light at the surface and thus prevent its passage into the containers.
Examples of prior art bottle coatings in general may be seen in U.S. Pat. Nos. 3,859,117; 3,937,853; 4,053,076; and 4,268,554.
Japanese Kokai 57-165466 (1982) and Japanese Kokai 61-209927 (1986) both disclose bottle coatings that include U.V. absorbers and may include dyes. There is no disclosure of selecting dyes that yield improved color fastness as in the present invention.
U.S. Pat. No. 3,519,462; 3,529,982; 3,870,519; 4,000,148; 4,319,016; 4,320,174; and 4,863,802 relate to U.V absorbers in resins and paints.
U.S. Pat. No. 4,557,730 discloses U.V. stabilization of dyes for fabrics.
U.S. Pat. No. 4,904,574 involves dyes that include metal complexes. The present invention specifically precludes metal-containing dyes because of the difficulties that metallic compounds cause in the recycling process.
The inclusion in coating compositions of additives to improve adhesion is generally known as shown in U.S. Pat. No. 4,409,266.